The terminology “copiers,” and “copies,” as well as “printers” and “prints,” is used alternatively herein. The terminology “imaging” and “marking” is used alternatively herein and refers to the entire process of putting an image, from a digital or analog source, onto a target substrate (e.g., paper). The image can then be permanently fixed to the target substrate by fusing, drying, or other means. It will be appreciated that the invention applies to multi-pass, multi-pitch marking architectures in any type of digital print system, including, but not limited to systems in the fields of incremental printing of symbolic information, photocopying, facsimile, and electro-photography. Digital print systems are also referred to by many technical and commercial names within these fields, including: electro-photographic (e.g., xerographic) printers, copiers, and multifunction peripherals; digital presses; laser printers; and ink-jet printers.
Digital print systems include paths through which sheets of a target substrate that are to receive an image are conveyed and imaged (i.e., the paper path). The process of inserting sheets of the target substrate into the paper path and controlling the movement of the sheets through the paper path to receive an image is referred to as “scheduling.”
One type of a multi-pass marking architecture is used to accumulate composite page images from multiple color separations. On each pass of the intermediate substrate, marking material for one of the color separations is deposited on the surface of the intermediate substrate until the last color separations is deposited to complete the composite image. Another type of multi-pass marking architecture is used to accumulate composite page images from multiple swaths of a print head. On each pass of the intermediate substrate, marking material for one of the swaths is applied to the surface of the intermediate substrate until the last swath is applied to complete the composite image. Both of these examples of multi-pass marking architectures perform what is commonly known as “page printing” once the composite page image is completed by transferring the full page image from the intermediate substrate to the target substrate.
Multi-pass printing may be scheduled in what may be referred to as “burst mode.” When scheduling in “burst mode,” sheets are inserted into, imaged, and output from the paper path at the maximum throughout capacity of the print system without any “skipped pitches” or delays between each consecutive sheet. A “pitch” is the portion (or length) of the paper path in the process direction which is occupied by a sheet of the target substrate as it moves through the paper path. A “skipped pitch” occurs when there is a space between two consecutively output sheets which is long enough to hold another sheet. Various methods for scheduling in burst mode known in the arts but are directed toward scheduling problems regarding duplex printing and integration of print engines with finishing devices.
In a multi-pitch marking architecture, the surface of the intermediate substrate (e.g., intermediate transfer drum or belt) is partitioned into multiple segments, each segment including a full page image (i.e., a single pitch) and an inter-document zone. For example, a two pitch drum is capable of printing two pages during a pass or revolution of the drum. Likewise, a three pitch Belt is capable of printing three pages during a pass or revolution of the belt. In a multi-pitch, multi-pass marking architecture, traditional “burst mode” scheduling starts accumulating images for each pitch of the intermediate substrate at the beginning of a print job and on the final pass of the multi-pass cycle each composite image is transferred to a target substrate.
However, problems can arise when attempting to transfer multiple composite images from the intermediate substrate, e.g., intermediate transfer drum or belt, to the target substrate, e.g., paper, during the same pass. These problems are primarily associated with integration of the intermediate substrate/transfer station with adjacent stations, e.g., preheating or other type of pre-conditioning stations and fusing stations, in the paper path. This is particularly a problem in a high-speed print system. For example: i) preceding stations, e.g., preheating or pre-conditioning stations, may not be able to operate properly if the target substrate is advanced at the same speed as in the transfer station, ii) likewise, successive stations, e.g., fusing stations, may not be able to receive the transferred sheets as fast as the transfer station can output them, iii) alternatively, to make the adjacent stations capable of such operation they may become unacceptably large and/or economically cost prohibitive. Furthermore, registration of sheets in the paper path to the composite page images on the intermediate substrate may not be sufficiently reliable if it is performed at the same speed as sheets advancing through the transfer station.
In many direct marking systems, particularly in multi-pass intermediate transfer systems, utilizing a two pitch intermediate drum architecture direct marking Solid Ink Jet (SIJ), Piezo Ink Jet (PIJ) to print at high speeds, page speed is often determined by jetting frequency, resolution in dots per inch (dpi), and/or the size of the inter-document zone (IDZ), i.e., the non-image or non-document zones or portions of the circumference of the intermediate drum. The result of such architecture gives rise to issue of setting the IDZ to a minimum with respect to image placement rather than paper placement. The reduction of the IDZ tends to increase print speed.
The IDZ is generally tied to drum size, i.e., average IDZ=(½ drum circumference) minus image width for a two document pitch drum. The nominal IDZ and drum size are chosen by, among other things, the ability to perform certain transition functions in IDZ time defined, in part, by: lateral or “x-axis” print head drive motion, the transfix roll engagement, and the Drum oiling and Maintenance (DMU) engagement. These subsystems preferably perform their intended actuations in the allocated IDZ time and space.
Some architectures are designed such that there is a blank border on the lead and trail edges of each document. Typically such a mandatory blank border might be 5 mm. However, many customer designed documents and originals actually have significantly larger borders, e.g., the Microsoft Word application defaults to 15-25 mm borders. Even though many systems are designed for the occasional 5 mm border, one can take advantage of the predominantly larger border of most documents while shortening the IDZ. Unfortunately, the drum must be sized for the smallest border. Furthermore, since in multi-pass intermediate direct marking architectures image drum passes must be synchronized with each other on the drum, there is little opportunity to reduce the IDZ within a document page. However, since the placement of successive documents need not be necessarily synchronized, the IDZ can be reduced wherever image borders allow; especially in systems wherein IDZ constraints are placed on image spacing rather than paper spacing.
What is needed in this art is a method of minimizing the inter-document zone for print architectures comprising multi-pass systems having different required start and stop durations for various transfer process subsystems.